- PakRat.
- Java RE (for running Java utilities)

1. Make sure you compiled your map with ready cubemaps.
2. Open PakRat (Java RE needed!).
3. In PakRat go ahead to folder with your map and open it.
4. You should find stuff like: "c<coords>" under "cubemapdefault.vtf", select all of them (only these with "c<coords>") and press "Delete" button and click "Yes to all".
5. Do the same thing with those under "cubemapdefault.hdr.vtf".
6. Place your map in your Source game (I recommend you GMod) and run the game on this map.
7. Type in console: building_cubemaps 1 and then buildcubemaps. You should see a really fast rendering images, these are your cubemaps. After it the game will restart map automatically.
8. If you did everything well your problem should be fixed!

Hope I helped